Yeah. ActivityPub has a type called 'Announce' that's used to make your followers aware of activity by another account. Mastodon uses it only for 'boosting' another user's content, but Lemmy's communities use it for everything ('Andrew has posted this comment', 'Andrew has Liked this post's, etc). Most of Lemmy's activities are ignored by Mastodon, but the Announce of a post or a comment is interpreted as a Boost.

It sort of works as a way to follow a community on Mastodon, but the individual boosting of all comments makes it annoying. I doubt anyone has set up a different account - you should be able to see the details of which actor is doing by clicking on it or hovering your mouse over it.

Anyway, speaking of jokes, have you heard how many MBIN users it takes to screw in a lightbulb?
Answer: 10. 1 to screw in the bulb, and 9 to tell you how great the software is. (I'm just kidding - there aren't 10 MBIN users, it just seems like there are because it evidently comes with a massive crowbar used to derail every thread to bollock on about it).